The invention relates to a multi-station communication bus system having at least one master station and at least one slave station. Any master station can include arbitration means for transmitting an arbitration signal per frame, and for detecting a negative or positive arbitration result, depending on an arbitration signal from any other station. Any master station can also include transmission means for transmitting a message after a positive arbitration result. The frame comprises a slave station address and a slave control signal, followed by a series of data byte spaces up to a predetermined maximum number per frame. The frame also includes space for indicating whether each byte is a last byte and for a data byte acknowledge signal for each byte. A system of this kind is known from Netherlands Patent Application 8002345 and the corresponding U.S. Pat. No. 4,429,384. The reference relates to a single-channel system; however, the invention is just as well useful to a more extensive system, for example with a separate clock wire. The bus may be galvanic or; realized by optical means. The arbitration means are effective in that the bus realizes a wired logic function, for example a wired AND-function. This can be done by means of an open collector connection of the stations and the like. Each station supplies a logic 0 then masks any logic 1 delivered by any other station. The operation is the same in the case of an optical system.
The known system is well-defined at the bit level, but does not describe the actions to be undertaken when one of two communicating stations is incapable of correctly processing the information applied to it in case of multi-byte messages.